284
neuromast innervation. Lateral line units also exhibited phase locking to boatwhistle vocalizations, with greatest spike rates exhibited at the onset of the call. These
results provide the fi rst direct evidence that oyster toadfi sh can use their lateral line
to detect behaviorally relevant sound stimuli, and potentially function in sound
localization (Radford and Mensinger 2014 ).
The lateral line responds to the near fi eld component of sound (particle motion)
and has the potential to contribute to hearing sensitivity and sound localization
(Mirjany et al. 2011 ). While delay lines such as found in the owl (Carr and Konishi
1988 ) have not been discovered, interneuromast distance, combined with afferent
nerve length and conduction velocities may be suffi cient to use sound delays to
locate the source. Anterior lateral line neuromasts can be separated by over 10 cm
with distances between anterior and posterior lateral line neuromasts capable of
exceeding 25 cm. For example, underwater sound (35 ppt, 20 °C) directly in front
of a 25 cm sl fi sh will impact the foremost anterior lateral neuromasts 16 μs prior to
arriving at neuromasts located at the base of the caudal fi n. However, factoring in
toadfi sh cranial nerve diameters [1–12 μm (Mensinger and Highstein 1999 )], conduction speeds associated with myelinated nerves of these diameters (10 or 50 m/s),
and afferent lengths to second order neurons (up to 5 cm length for anterior and
20 cm for posterior; Mensinger unpublished), delays to the central nervous system
would range from approximately 400 μs to 2 ms, which is within the time frame
used for interaural delays found in other vertebrates.
4 Discussion
4.1 Detection Distance
The experiments demonstrate that the utricle and lateral line are well designed to
detect toadfi sh vocalizations and they may play a role in sound localization.
However, it remains unclear what is the functional range of each system, how acoustic input to both systems is integrated, and the effect of self-generated movement on
hearing sensitivity. Male toadfi sh often nest in high densities (up to 10–12 m
2 ) in
estuaries near Woods Hole, MA, and produce loud [~140 dB re 1 μPa (Tavolga
1971 )] boatwhistles with fundamental frequencies ranging between 90 and 250 Hz
depending on season and geographical location (Fine 1978 ), which is within the
sensitivity and range for the utricle and lateral line. Calls can propagate several
meters underwater with distance infl uenced by toadfi sh size, water depth, and substrate composition (Fine and Lenhardt 1983 ) with hydrophones able to detect calls
at least 5 m from toadfi sh nests (Mensinger 2014 ), although it remains to be determined at what range the females can detect the signal or what aspect of the boatwhistle infl uences mate choice.
Underwater acoustic stimulus consists of two components, the “nearfi eld,” which
is dominated by hydrodynamic fl ow and the “farfi eld,” which is modulated by the
A.F. Mensinger
neuromast innervation. Lateral line units also exhibited phase locking to boatwhistle vocalizations, with greatest spike rates exhibited at the onset of the call. These
results provide the fi rst direct evidence that oyster toadfi sh can use their lateral line
to detect behaviorally relevant sound stimuli, and potentially function in sound
localization (Radford and Mensinger 2014 ).
The lateral line responds to the near fi eld component of sound (particle motion)
and has the potential to contribute to hearing sensitivity and sound localization
(Mirjany et al. 2011 ). While delay lines such as found in the owl (Carr and Konishi
1988 ) have not been discovered, interneuromast distance, combined with afferent
nerve length and conduction velocities may be suffi cient to use sound delays to
locate the source. Anterior lateral line neuromasts can be separated by over 10 cm
with distances between anterior and posterior lateral line neuromasts capable of
exceeding 25 cm. For example, underwater sound (35 ppt, 20 °C) directly in front
of a 25 cm sl fi sh will impact the foremost anterior lateral neuromasts 16 μs prior to
arriving at neuromasts located at the base of the caudal fi n. However, factoring in
toadfi sh cranial nerve diameters [1–12 μm (Mensinger and Highstein 1999 )], conduction speeds associated with myelinated nerves of these diameters (10 or 50 m/s),
and afferent lengths to second order neurons (up to 5 cm length for anterior and
20 cm for posterior; Mensinger unpublished), delays to the central nervous system
would range from approximately 400 μs to 2 ms, which is within the time frame
used for interaural delays found in other vertebrates.
4 Discussion
4.1 Detection Distance
The experiments demonstrate that the utricle and lateral line are well designed to
detect toadfi sh vocalizations and they may play a role in sound localization.
However, it remains unclear what is the functional range of each system, how acoustic input to both systems is integrated, and the effect of self-generated movement on
hearing sensitivity. Male toadfi sh often nest in high densities (up to 10–12 m
2 ) in
estuaries near Woods Hole, MA, and produce loud [~140 dB re 1 μPa (Tavolga
1971 )] boatwhistles with fundamental frequencies ranging between 90 and 250 Hz
depending on season and geographical location (Fine 1978 ), which is within the
sensitivity and range for the utricle and lateral line. Calls can propagate several
meters underwater with distance infl uenced by toadfi sh size, water depth, and substrate composition (Fine and Lenhardt 1983 ) with hydrophones able to detect calls
at least 5 m from toadfi sh nests (Mensinger 2014 ), although it remains to be determined at what range the females can detect the signal or what aspect of the boatwhistle infl uences mate choice.
Underwater acoustic stimulus consists of two components, the “nearfi eld,” which
is dominated by hydrodynamic fl ow and the “farfi eld,” which is modulated by the
A.F. Mensinger